The field of this invention relates to ion exchange systems utilizing moving folded beds for loading and regeneration of the resin granules. More particularly, this invention relates to improvements in the metered transfer of resin increments as expelled from the loading and/or regeneration columns.
Higgins U.S. Pat. No. 2,815,322 is one of the earliest patents describing a moving folded bed ion exchange system. The resin is transferred around a continuous loop by means of hydraulic pulses. A columnar section of the loop provides a continuous bed, the upper portion of which is the loading section and the bottom portion the regeneration section. A freeboard space is provided at the top of the columnar section above the top of the resin bed, the level being controlled by a spill-over outlet which transfers resin to a receptacle section for return to the bottom of the regeneration section. Since all of the resin in the circuit is moved with each hydraulic pulse, there is an automatic metering or balancing of the transferred resin. Such an arrangement, however, provides no separation between the different sections of the loop so that liquids being processed in the loading section become contaminated with the liquids employed for regeneration. Also, movement of all of the resin with each pulse requires the use of relatively high pressures for the hydraulic pulses, and the resin granules during movement are subjected to undesirable frictional attrition, which shortens the useful life of the resin.
Later Higgins patents such as U.S. Pat. No. 3,579,322, disclose continuous loop systems in which sections of the loop are divided into separate compartments with valves between the compartments. As illustrated by U.S. Pat. No. 3,579,322 the pulsing of a resin increment into the bottom of the loading compartment causes the ejection of resin increment of corresponding volume from the top of the loading colunn into a receiver compartment. With this arrangement, only part of the resin in the system is moved with each pulse, and a greater separation is provided between the loading and regeneration sections of the system. The system is operated with the resin moving upwardly in a completely filled loading column, and with the resin moving downwardly in the partially filled regeneration compartments. No means is provided for precisely metering the resin increments transferred between the different compartments of the system.
More recently, an improved folded bed ion exchange system has been disclosed in Carlson U.S. Pat. Nos. 4,208,904 and 4,228,001. In this system, separate vertically-extending columns are provided for the loading and regeneration operations, and separate receivers are provided in each of the circuits between the loading and regeneration columns. Both of the columns are provided with freeboard spaces above the tops of the resin beds therein, the level being controlled by spill-over type outlets through which the resin is transferred to its respective receiver. Both columns are operated with the incoming increments of resin introduced into the bottoms of the columns and moving upwardly in the columns to the top outlets. Liquid is added to the resin increments to facilitate their transfer as slurries of the resin granules. No means is provided for precise metering of the volume of the transferred resin increments, nor any means for balancing the increments transferred from or to the loading column in relation to the resin increments transferred from or to the regeneration column.
A further improvement in folded bed ion exchange systems is disclosed in the pending patent application of Harold N. Hedrick and Solon G. Whitney, Ser. No. 275,658, filed June 22, 1981, now U.S. Pat. No. 4,385,993 which is co-owned with the present application and for which the issue fee has been paid. The corresponding European Patent Application has been published under EPA Publication No. 0068413. This system utilizes separate treatment and pulse chambers between the columns in which each portion of the circuit, and operates with the columns completely filled with compacted resin granules. The introduction of pulsed increments of granules into the bottoms of the loading and stripping columns expells increments of corresponding volume from the tops of the columns. Therefore, the volume of resin pulsed into the bottom of each column is subject to separate control, but no means is provided for precisely controlling the volumes of resin transferred in each pulse, nor is any means provided for balancing the resin increments transferred to each part of the circuit.